The present invention relates to a light emitter and a method for manufacturing the same.
In recent years, semiconductor light emitters such as LEDs which emit light in a range from ultraviolet to visible light have been realized by using nitride semiconductor materials typified by GaN, AIN, InN or a mixed crystal thereof.
These LEDs mainly utilize a sapphire substrate which is an insulator as a substrate. Therefore, different from ordinary light emitters, the LED is required to have both p-type and n-type electrodes on its surface and various structures have been proposed for this purpose.
A conventional light emitter using a nitride semiconductor material will be detailed with reference to FIGS. 7(a) and 7(b).
In a light emitter shown in FIGS. 7(a) and 7(b), an n-GaN layer 2, an InGaN light emitting layer 3, a p-GaN layer 4 and a p-transparent electrode 6 are sequentially formed on a sapphire substrate 1. As regards the n-Gan layer 2, in a partial region thereof, a part of the surface of thereof is removed together with the InGaN light emitting layer 3 and the p-GaN layer 4 which are formed thereon. An n-bonding electrode 5 is directly connected to the region. Further, a p-bonding electrode 7 is connected on a partial region of the p-transparent electrode 6. Moreover, balls 8 and bonding wires 9 are connected to the n-bonding electrode 5 and the p-bonding electrode 7.
In such a structure that both the p- and n-electrodes are drawn from a surface of a device, electric current basically flows in parallel directions with interfaces of semiconductor layers in the device. Therefore, electric current flowing from a p-type layer through the light emitting layer to an n-type layer hardly flows evenly through each part of the light emitting layer. As a result, distribution of light emission intensity in a light emitting portion tends to be wide-spread.
To cope with this problem, the p-electrode may be formed on an almost entire surface of the light emitting layer 3. In order to let emitted light out of the light emitting layer 3, the p-electrode must be a transparent electrode. Accordingly, there is no choice but to use an extremely thin film, for example, a metal film of about 10 nm in thickness. However, it is difficult to bond wires on such an extremely thin film. Therefore, in the above-described light emitter, the p-transparent electrode 6 is formed as the p-electrode and the p-bonding electrode 7 which has enough thickness and is opaque is formed on a part thereof
However, in the above-described light emitter, even though the layered structure thereof is contrived so that the emitted light can be taken out from an upper surface of the light emitter, it is still difficult to let out the light emitted just under the opaque p-bonding electrode 7. That is, even if the p-transparent electrode 6 is provided on the entire surface of the light emitting layer 3, the light emitted just under the p-bonding electrode 7 cannot be taken out because it is blocked by the p-bonding electrode 7. Therefore, it is a problem that an improvement in letting out the emitted light is not brought about.
According to the present invention, provided is a light emitter comprising:
a substrate, at least one semiconductor layer of a first conductivity type formed on the substrate,
at least one semiconductor layer of a second conductivity type formed on a partial region of the semiconductor layer of the first conductivity type,
a first bonding electrode connected to the semiconductor layer of the first conductivity type, and
a second bonding electrode connected to an almost entire surface of the semiconductor layer of the second conductivity type,
the light emitter being characterized in that the substrate is transparent to light emitted from a proximity of a junction between the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type,
the second bonding electrode is formed to have an almost rectangular shape and a substantially minimum area for bonding, and
sides of the emitter are disposed in three directions of the circumference of the second bonding electrode.
Further, according to the present invention, provided is a light emitter provided with;
a substrate,
at least one semiconductor layer of a first conductivity type formed on the substrate,
at least one semiconductor layer of a second conductivity type formed on a partial region of the semiconductor layer of the first conductivity type,
a first bonding electrode connected to the semiconductor layer of the first conductivity type, and
a second electrode connected to an almost entire surface of the semiconductor layer of the second conductivity type,
the light emitter being characterized in that the substrate is transparent to a light emitted from a proximity of a junction between the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type,
the second electrode includes a second bonding electrode and a second transparent electrode,
the second bonding electrode is formed to have an almost rectangular shape and a substantially minimum area for bonding, and
sides of the emitter are disposed in three directions of the circumference of the second bonding electrode.
Still further, according to the present invention, provided is a process for manufacturing a light emitter comprising:
forming at least one semiconductor layer of a first conductivity type, at least one semiconductor layer of a second conductivity type, a first bonding electrode and a second bonding electrode, in plural numbers in a longitudinal and a transverse direction on a substrate, the semiconductor layers of the first conductivity type and of the second conductivity type and the first and second bonding electrodes being to constitute a plurality of light emitters; and
separating the resulting substrate into units of light emitters,
wherein the semiconductor layers and the electrodes are disposed in such a manner that, in the longitudinal direction, the first bonding electrodes are in juxtaposition with each other and the second bonding electrodes are in juxtaposition with each other, and in the transverse direction, the first bonding electrodes are adjacent to the second electrodes.